Various forms of accelerometers have been built using an analog force rebalance principle. Analog accelerometers have the associated inaccuracies of conversion of an analog signal into a digital signal for computer usage. In particular, analog-to-digital converters suffer resolution and aliasing problems, and voltage-to-frequency converters suffer bias, scale factors and sometimes quantization inaccuracies. Some directly digital compatible accelerometers have been built using single and dual beam resonating elements. The single beam accelerometers require difficult crystal isolation techniques. A dual beam resonating element design substantially overcomes the isolation problem. However, both size and g range have been large with conventional vibrating beam accelerometers, such accelerometers typically being one cubic inch in size for a g range of 40-120. A smaller volume, of about 0.25 cubic inches is desirable in a low g range (.+-.4 g) accelerometer.
One approach to a small vibrating beam accelerometer is shown in U.S. Pat. No. 4,479,385. This patent describes an accelerometer consisting of two resonator members and a spacer mass. As the pendulum of the accelerometer bends, the strain in each element is used to change the resonant frequency of the beams. This configuration has the advantage of small size, and of adjustable g range by changing the mass and/or spacer thickness. However, it does suffer from several disadvantages. In particular, it has sensitivity to accelerometer along both transverse axes, although such sensitivity is typically attenuated 50-100 times. Furthermore, the dual beam arrangement will cross-couple frequency and then "lock-in" for some range of mid-band frequencies. The accelerometer as shown has no form of damping, and so will resonate at some natural frequency of acceleration input with an unacceptably high Q.